Test: Intermolecular Forces (Old NCERT) - Bank Exams MCQ

1. In Case of option (a), We have polar ammonia NH₃ but non polar CH₄, tetrahedral and all forces balanced, so weak attraction between the two.

2. Option (B) is correct.
NH₃ is a fairly polar molecules due to the strong electronegativity of N and its pyrimidal shape with a lone pair of electrons at the peak. So two of the molecules have a strong attraction for one another. 

3. In Case of option (c), both molecules being non polar due to symetrical structure in tetrahedrons .

4. In Case of option (d), both molecules are non polar, structure is O=C=O 

Intermolecular force can only be Vaan der Waals force acting between two molecules.

Thermal energy is the energy of a body arising from motion of its atoms or molecules. It is directly proportional to the temperature of the substance. It is the measure of average kinetic energy of the particles of the matter and is thus responsible for movement of particles. This movement of particles is called thermal motion. We have already learnt that intermolecular forces tend to keep the molecules together but thermal energy of the molecules tends to keep them apart. Three states of matter are the result of balance between intermolecular forces and the thermal energy of the molecules.

In a gas, the distance between molecules, whether monatomic or polyatomic, is very large compared with the size of the molecules; thus gases have a low density and are highly compressible.

Density: The molecules of a liquid are packed relatively close together. Consequently, liquids are much denser than gases.

Chemical bonding forces are not considered to be part of van der Waals forces. Van der Waals forces include London forces, dipole-dipole forces, and dipole-induced dipole forces.

Dipole-dipole interaction energy between stationary polar molecules is proportional to 1/ r³ and that between rotating polar molecules is proportional to 1/ r⁶ where ‘r’ is the distance between polar molecules

Besides dipole - dipole interaction, polar molecules can interact by London forces also.

All of the above are the properties of gases.

London dispersion forces operate only over very short distance. The energy of interaction varies as
1/(distance between two interacting particles)⁶ 

Large or more complex the molecules, greater is the magnitude of London forces.

This is obviously due to the fact that the large electron clouds are easily distorted or polarised.
Hence, greater the polarisability of the interacting particles, greater is the magnitude of the interaction energy.

Hydrogen bonding is a type of attractive force that occurs between molecules when a hydrogen atom is covalently bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. In water molecules, hydrogen bonding occurs between the positively charged hydrogen atoms of one water molecule and the negatively charged oxygen atoms of another water molecule. These hydrogen bonds cause the water molecules to attract each other and stick together, which gives water many of its unique properties, such as its high surface tension and its ability to act as a solvent. The hydrogen bonds do not cause the water molecules to repel each other or to compactly arrange, but they do make it more difficult for the molecules to slide over each other, which contributes to the high viscosity of water.

A hydrogen bond is a partially electrostatic attraction b/w a hydrogen atom which is bound to a more electronegative atom such as N, O and F etc. And also hydrogen bonding occurs only b/w molecules in which H atom bounded to a electronegative atom.

Partial charge is a small charge developed by displacement of electrons. It is less than unit electronic charge and is represented as δ⁺ or δ^–  

HF - Hydrogen bonding HCl,HBr,HI→ Dipole-dipole interaction, London-dispersion force.

It is because of hydrogen bonding . Since F is the most electronegative element , its hydrogen bonding tendency is strongest which makes boiling point of HF increase.